There are already several pen-based handheld computer products on the market for the storage and manipulation of personal data. Examples of these are the Apple Newton, the Tandy Zoomer and the Amstrad PenPad. In these products the user has to become familiar with several unrelated mechanisms in order to perform manipulations on the data stored in the device. The term `manipulations` refers to operations such as moving, deleting, copying etc of data. In addition, the methods of selecting data for manipulation usually effect only a transient selection so that further manipulation of the same data requires the data to be reselected.